Navy Cmdr. Donal M. Billig yesterday recounted step by step his performance in the five heart operations that led to involuntary manslaughter charges against him, acknowledging that in one instance he tore a patient's heart tissue and later changed his technique because of that surgery.

Billig, 54, the former head of cardiothoracic surgery at Bethesda Naval Hospital, spent his second full day on the stand in his court-martial. He presented himself as a competent surgeon who followed and preached the motto, "Don't ever do anything to a patient you wouldn't have done to yourself."

In the case of that patient whose tissue was torn -- and whose heart was too swollen from surgery to allow doctors to close his chest -- Billig said his decision to move the patient from the operating room with his chest open and packed with gauze was acceptable practice. He denied prosecution testimony that he left the critically ill patient for two hours in the intensive care unit.

"I know I saw that patient in ICU . . . because I have a very visual mental picture of [retired Air Force Lt. Col. John L.] Kas with his dressings and swollen face," said Billig. Kas died that night after Billig attempted to repair his bleeding heart in the intensive care unit.

In one of the other cases, Billig said the patient's death may have been caused because a nurse turned off the pacemaker. And in a third, he said a supervising surgeon did not stop or correct Billig's technique in the operating room.

Testimony from Billig, who also is charged with 24 counts of dereliction of duty for performing operations without supervision, constitutes the crux of the defense case.

The prosecution produced more than 40 witnesses during five weeks to support its contention that Billig was incompetent, handicapped by poor eyesight and operated without full hospital credentials.

The case has unfolded during the last year, coming in the midst of several other negative reports on the quality of medical facilities and service in the military.

Billig, who maintained a confident, assured manner during the seven hours of defense questioning and two in cross-examination, said that "everybody makes mistakes," indicating, for example that surgeons mistook a vein for an artery in the Kas operation. But he argued that the death of a patient does not indicate a failure by the physician and maintained that his own techniques in all of the cases were safe and acceptable.

"It's difficult as a surgeon and a doctor to try to defend what I did when five people died and say it was wonderful," Billig said, "[but] other surgeons would have acted similarly . . . . Everything was done to the best of my ability."

At one point in the morning, Billig took off his uniform jacket, rolled up his shirt sleeves and demonstrated his surgical technique at a makeshift operating table set up with cardboard boxes before the panel of nine officers.

"I'm sorry I shook a little bit, but I was kind of nervous," Billig said after the 10-minute demonstration. He then asked for a recess to regain his composure.

Under cross-examination, Billig answered more questions on his whereabouts after the Kas surgery. He had testified earlier that he believed he had remained at the hospital.

"Is it possible that you went to your home with a patient bleeding to death?" asked the prosecutor, Lt. Cmdr. Joseph G. VanWinkle.

"Anything is possible," answered Billig.

"Does your vision [of Kas in the] intensive care unit include blood on the floor and people tracking it around?" asked the prosecutor, alluding to testimony that the patient bled profusely during Billig's absence.

"No, it does not, but that could have been the case," answered the doctor.